package com.kyrioscraft.cloud.thead.jdklab.tools.forkjoin;

import java.util.ArrayList;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.RecursiveTask;

/**
 * @Author kyrioscraft
 * @Date 2019/2/19 15:29
 * @Description //TODO
 **/
public class CountTask extends RecursiveTask<Long> {
    private static final int THRESHOLD = 10000;
    private long start;
    private long end;

    public CountTask(long start, long end) {
        this.start= start;
        this.end = end;
    }


    @Override
    protected Long compute() {
        long sum = 0;
        boolean canCompute = (end-start)<THRESHOLD;
        if(canCompute) {
            for(long i=start; i<=end; i++) {
                sum +=i;
            }
        } else {
            //分成100个小任务
            long step = (start+end)/100;
            ArrayList<CountTask> subTasks = new ArrayList<>();
            long pos = start;
            for(int i=0; i<100; i++) {
                long lastOne = pos+step;
                if(lastOne>end) lastOne=end;
                CountTask subTask = new CountTask(pos,lastOne);
                pos+=step+1;
                subTasks.add(subTask);
                subTask.fork();
            }
            for(CountTask t: subTasks) {
                sum +=t.join();
            }
        }
        return sum;
    }

    public static void main(String[] args) {
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        CountTask task = new CountTask(0,200000L);
        ForkJoinTask<Long> result = forkJoinPool.submit(task);
        try{
            long res = result.get();
            System.out.println("sum="+res);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
    }
}
